2. The apparatus As shown in figure 1 and the accompanying photograph (figure 2), the subject of investigations is a rectangular glass or acrylic block of dimensions length (l) × width (w) × thickness
(t) ~ 120 mm ×70 mm × 20 mm. A suitable ray of light is provided by a 1 mW red laser capsule which runs on 2AAA batteries. The laser capsule is mounted centrally on an arm which can be rotated in the horizontal plane about a pivot, so that the laser beam is incident on the glass block at the pivot point with variable angles of incidence. To facilitate measurement of angles of incidence, the line taken by the laser beam is marked by a corresponding line on the arm on which it is mounted, which moves under a transparent 150 mm plastic protractor fixed to the base plate and centred on the pivot point. The reference line on the arm can then be viewed through the protractor, and the angle of incidence read off. For reflection studies a small vertical white
Studies